Electric resistance heating devices – Heating devices – Immersion heater details
Patent
1993-03-16
1995-10-17
Walberg, Teresa J.
Electric resistance heating devices
Heating devices
Immersion heater details
392501, H05B 382
Patent
active
054598125
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electric immersion heaters.
Traditionally, electric immersion heaters which are used, for example, in kettles, hot water jugs, washing machines, dishwashers and other water heating appliances comprise a metal sheathed element which is brazed to a metal element head which is mounted to overlie and is sealed with respect to an opening in a wall of a liquid containing chamber of an appliance. The element is brazed to the head at both its end portions, where the element sheath extends through the head to project by a small amount on the dry side of the head. The element is formed so that a so-called hot return portion, which is a portion intermediate the ends, .is bent back against the head and brazed thereto. As shown, for example in GB 2052227, a thermally-sensitive actuator of a control is commonly arranged in thermal contact with the side of the head opposite the hot return i.e. the dry side, so that should the element overheat, for example when the appliance is switched on dry or boils dry, the temperature rise in the hot return portion of the element is conducted through the head to the actuator which, at a predetermined temperature, operates the control to interrupt the power supply to the element and thus de-energises the element.
In GB 892685 which relates to electric kettles, the hot return portion is not brazed to the head directly but rather to a copper stud which is carried by the head. A copper screw engages with the stud through the head and in turn locates a copper plate which mounts a two part bimetallic actuator which, in the event that the element overheats, opens a switch. This is a complicated construction of high thermal capacity with a long thermal path between the element and the actuator, and accordingly has a very slow response time to a dry switch on or boil dry condition.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an electric immersion heater includes a metal sheathed heating element formed to provide two end portions and an intermediate return portion adjacent the end portions. The electric immersion heater further includes a heat conduction link of sheet material of high thermal conductivity attached at a first end to and extending substantially completely around the return portion of the element in good thermal contact therewith. A second end of the heat conduction link and the end portions of the element are arranged so that in use they are adapted to extend through a sealing means disposed in at least one opening in a wall of a liquid heating chamber such that, from outside the chamber, electrical connections can be made to the end portions of the element and thermally-responsive control means can be associated with the second end of the heat conduction link.
By utilising a heat conduction link of sheet material the surface area for transfer of heat from the element to the link is large compared with the thermal conduction cross-sectional area of the link. A quick response to a boil-dry or switch-on-dry condition is thus ensured. Also by providing a short length of the link within the chamber exposed to liquid therein, the large surface area of the link over this length relative to its conductive cross-sectional area will result in the free end of the link reflecting the temperature of the liquid within the chamber so that a multi-purpose control can be provided which serves to control the temperature of the liquid in normal operation in addition to fulfilling its safety function in a boil or vaporise-dry or switch-on-dry condition.
In a preferred arrangement, the link is at least five times as wide as it is thick in the region of contact with the element, whereby a large area of contact is obtained, relative to the heat-transmitting cross sectional area of the link.
Preferably, the link is made from copper, although other high thermal conductivity materials could be used. It may also be plated, or clad with stainless steel, for example, if required for purposes of strength and appearance. Where the cladding is of a l
REFERENCES:
patent: 2802921 (1957-08-01), Miklas
patent: 2977454 (1961-03-01), Volker
patent: 3715567 (1973-02-01), Mandziak
patent: 4041433 (1977-08-01), Watson
patent: 4068116 (1978-01-01), McKinstry
patent: 4730099 (1988-03-01), Bleckman
patent: 4835366 (1989-05-01), Owen et al.
Strix Limited
Walberg Teresa J.
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